Hi Chris,
My goal is a low latency USB microphone that's always on; similar to an intercom system.
I am capturing data from my microphone, and transmitting it via pcm_write() to the USB gadget card, and arecording on the USB host. If I query the buffer, I begin to see a creeping fill on the device side buffers, such that after a few hours of constant streaming, the buffer is filled, and my pcm_write is returning "we only wrote SOME of your data". As this happens, I start to notice more and more latency between my device's capture and the host's playback, as I eventually have a whole buffer's worth of "old" audio I'm queuing "now's audio" data behind. If I modify the UAC driver to provide a larger buffer size, my pcm_write of "not a full buffer" takes longer to happen, but when it does, my latency has gone from unnoticeable to several seconds.
I figured (and may very well be wrong), that this was due to my device clocks sending buffers at a rate *slightly* faster than the USB is able to sink it to the host. Could this be something else?
Thanks,
Rob
On Thu, Jul 12, 2018 at 8:13 PM, chris hermansen <clhermansen@xxxxxxxxx> wrote:
Rob and list,On Thu, Jul 12, 2018, 19:27 Rob <alsa@xxxxxxxxxxxxx> wrote:Hi all,I'm reading about the feedback mechanism for USB audio. I'm trying to see if I can implement asynchronous mode.What makes you think asynchronous mode isn't already implemented?Chris Hermansen
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